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Sum of the Sequence
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abhijith reddy  
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 More options Nov 4, 12:53 am
From: abhijith reddy <abhijith200...@gmail.com>
Date: Tue, 3 Nov 2009 21:53:55 -0800 (PST)
Local: Wed, Nov 4 2009 12:53 am
Subject: Sum of the Sequence
Is there a way to find the sum of the Kth series ( Given below)

K=0   S={1,2,3,4,5,6,....}
K=1   S={1,2,4,7,11,16..}  common diff = 1,2,3,4 5 ...
K=2   S={1,2,4,8,15,26...} common diff = 1,2,4,7 11... (series with
K=1)
K=3   S={1,2,4,8,16,31...} common diff = 1,2,4,8 15... (series with
K=2)

Note that the common difference of Kth series is the (K-1) series

Any ideas ??


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Prunthaban Kanthakumar  
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 More options Nov 6, 12:20 am
From: Prunthaban Kanthakumar <pruntha...@gmail.com>
Date: Fri, 6 Nov 2009 10:50:14 +0530
Local: Fri, Nov 6 2009 12:20 am
Subject: Re: [algogeeks] Sum of the Sequence

This is a 'finite calculus' (differences & summations) problem.
You can solve it using difference operator (actually its inverse which gives
you the discrete integration which is nothing but summation).
If you do not know finite calculus, Google for it (or refer Concrete
Mathematics by Knuth).

The solution for any k is.

*f(n) = nC(k+1) + nC(k-1) + nC(k-3) + .... (all the way down to nC0 or nC1
depends on k is odd or even).*

Here nCr is the binomial coefficient "n choose r".

Eg: Let k = 3, n = 4

f(4) = 4C4 + 4C2 + 4C0 = 1 + 6 + 1 = 8

Another, k = 3 and n = 5

f(5) = 5C4 + 5C2 + 5C0 = 5 + 10 + 1 = 16

On Wed, Nov 4, 2009 at 11:23 AM, abhijith reddy <abhijith200...@gmail.com>wrote:


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Prunthaban Kanthakumar  
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 More options Nov 6, 12:30 am
From: Prunthaban Kanthakumar <pruntha...@gmail.com>
Date: Fri, 6 Nov 2009 11:00:10 +0530
Local: Fri, Nov 6 2009 12:30 am
Subject: Re: [algogeeks] Sum of the Sequence

On a related note,
The solution I gave you is to find the nth element in the kth series.
If you want to sum the first 'n' elements of the kth series (call the
function s(n,k)), then it is easy to see that,

*s(n,k) = f(n+1, k+1) - 1*

where f(n+1, k+1) is the (n+1)th element in the (k+1)th series.
This can also be easily done using the summation operator of 'finite
calculus'.

On Fri, Nov 6, 2009 at 10:50 AM, Prunthaban Kanthakumar <


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abhijith reddy  
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 More options Nov 6, 1:05 am
From: abhijith reddy <abhijith200...@gmail.com>
Date: Fri, 6 Nov 2009 11:35:09 +0530
Local: Fri, Nov 6 2009 1:05 am
Subject: Re: [algogeeks] Sum of the Sequence

Thank you so much ! :)

On Fri, Nov 6, 2009 at 11:00 AM, Prunthaban Kanthakumar <


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nikhil garg  
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 More options Nov 7, 1:52 am
From: nikhil garg <nikhilgar...@gmail.com>
Date: Sat, 7 Nov 2009 12:22:24 +0530
Local: Sat, Nov 7 2009 1:52 am
Subject: Re: [algogeeks] Sum of the Sequence

Thanks a ton. I found finite calculus very interesting and useful !

On Fri, Nov 6, 2009 at 11:35 AM, abhijith reddy <abhijith200...@gmail.com>wrote:

--
nikhil-

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